1. Field of the Invention
This invention relates generally to vapor recovery control for gasoline pumps and particularly to an improvement to a fuel dispensing nozzle of a conventional service station fuel pump used in replenishing the tank with fuel. The improvement relates to an assembly which attaches to the tubular fuel dispensing nozzle and functions to prevent fuel vapor displaced from the head space of the vehicle fuel tank from being discharged into the atmosphere during a refueling operation.
2. Description of the Prior Art
In the 1920's automobile manufacturers and oil refiners discovered that the addition of tetraethyl lead to gasoline reduced engine "knocking" by slowing the rate at which gasoline ignited. The ability of gasoline to resist knocking is measured by its octane number. The higher the octane number, the greater the resistance to knocking. As the compression ratio of gasoline engines increase, so too does the minimum octane requirement.
During the 1960's oil companies began adding more lead to gasoline in order to increase the octane level of gasoline required by the automobile industry's production of more "muscle cars" (high compression engines with greater horsepower). The increasing amount of lead, however, resulted in a commensurate increase in lead emissions into the environment, creating a major public health hazard.
Partly in response to this hazard Congress, in the Clean Air Act of 1970, established air quality standards for lead and required automobile manufacturers to reduce carbon monoxide and hydrocarbon exhaust emissions through the use of catalytic converters (in 1975). Because leaded gasoline contaminated catalytic converters, oil refiners were forced to manufacture gasoline without lead.
With the mandated phase-out of lead as an octane booster, the major oil companies turned to high-octane aromatics--benzene, toluene, and xylene. Between 1980 and 1988, aromatic content of gasoline increased from about 22 to 32 volume percent. Similarly, the amount of benzene in gasoline also increased sharply over the same period (from about 1.75% to about 2.4%). But benzene, despite its chemical properties and many industrial uses, is a carcinogen. It causes cancer.
By far the most extensive operations resulting in benzene exposure to the general population are gasoline stations, of which there are about 200,000 in the United States. Most of the vapor liberated during a typical fill-up operation results from the displacement of benzene trapped within the gas tank, and not from the gasoline being pumped. Recent measurements in U.S. self-service stations found benzene levels averaging 250 ppb immediately adjacent to the gas pumps. It is estimated that about 37 million people are intermittently exposed to such benzene levels through the use of self-serve facilities. According to the Environmental Protection Agency, consumers who use self-service pumps are regularly exposed to more than one ppm during the time they are in the service-station area. Gasoline attendants, of course, are continuously exposed to them. The Office of Technology Assessment of the U. S. Congress states that refueling emissions are the last significant source of vehicle emissions to remain largely uncontrolled.
Two primary approaches have been taken to deal with this problem: on-board canisters in automobiles and vapor recovery controls for gasoline pumps (Stage II). On-board recovery systems involve canisters of vapor adsorbent material carried on the automobile through which gasoline tank vapors are routed during refueling. Examples are provided in U.S. Pat. Nos.: 4,798,306; 4,809,863; 4,809,865; 4,813,453; 4,815,436; and 4,836,835.
The choice between Stage II vapor recovery systems at gasoline stations and on-board refueling emission control systems on motor vehicles has been debated for over ten years. While both approaches are technologically feasible and cost effective, the California Air Resources Board determined on-board control will not be as effective as the Stage II service station measure at reducing individual fueling risk or reducing areawide and neighborhood benzene exposure for the next 15 to 20 years (until the controlled vehicles replace uncontrolled vehicles). Data demonstrate that vapor recovery systems at the gasoline pump can sharply reduce, by a factor of 10 (from 1.5 ppm to 0.13 ppm), benzene exposure for both motorists and service station attendants.
Implementation of Stage II service station vapor recovery systems has been mandated in only a few states. (In 1987, in order to reduce ambient concentrations of benzene, the State of California finalized regulations requiring refueling controls at all service stations with a monthly gasoline throughput of over 240,000 gallons per year.) The primary obstacles to widespread implementation is the expense and inconvenience of replacing existing equipment. This expense and inconvenience would be minimized by the availability of technology for adapting existing service station pumping equipment to function as a Stage II vapor recovery system.
It is the object of the present invention to provide a fuel dispensing nozzle assembly which, upon attachment to the tubular nozzle of a standard gasoline pump dispensing gun, adapts the pumping unit to act as a Stage II vapor recovery system.